1. Field of the Invention
The present invention generally relates orienting perforating guns in oil and gas extraction. Specifically, the invention attempts to externally orient perforating guns in a desired direction with an external member and internally correcting with a pivot mechanism.
2. Prior Art Background
The process of extracting oil and gas typically consists of operations that include preparation, drilling, completion, production, and abandonment.
Preparing a drilling site involves ensuring that it can be properly accessed and that the area where the rig and other equipment will be placed has been properly graded. Drilling pads and roads must be built and maintained which includes the spreading of stone on an impermeable liner to prevent impacts from any spills but also to allow any rain to drain properly.
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling the wellbore is lined with a string of casing. An annular area is thus formed between the string of casing and the wellbore. A cementing operation is then conducted in order to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
The first step in completing a well is to create a connection between the final casing and the rock which is holding the oil and gas. There are various operations in which it may become necessary to isolate particular zones within the well. This is typically accomplished by temporarily plugging off the well casing at a given point or points with a plug.
A gun string assembly is positioned in an isolated zone in the wellbore casing. The gun string assembly comprises a plurality of perforating guns coupled to each other either through tandems or subs. The perforating gun is then fired, creating holes through the casing and the cement and into the targeted rock. These perforating holes connect the rock holding the oil and gas and the well bore.
The perforating gun comprises a conveyance for the shaped charges such as a hollow carrier, a tube to align and hold the shaped charges (charge holder tube), charge holder tube end plates, shaped charges, detonating cord, and the detonator. In deviated/horizontal wellbore perforating applications, it is sometimes desirable to orient the direction of the perforation tunnels within the wellbore, so that more perforations can be concentrated in a particular direction with respect to a deviated/horizontal wellbore, either up, down, up and down, or to one side or the other.
Prior Art System External Orientation Overview (0100)
As generally seen in the system diagram of FIG. 1 (0100), prior art systems associated with perforation gun assemblies include a wellbore casing (0120) laterally drilled into a wellbore. A gun string assembly (GSA) comprising plural perforating guns (0101, 0102) with detonation train is positioned in a hydrocarbon fracturing zone. The guns may be coupled to each other with a tandem (0104). External methods, where a fin or a protuberance (0103) from the perforating gun causes the center of mass of the assembly to be such that the perforating gun tends to be on the low side of the wellbore casing and oriented with the fins to the high side of the wellbore as the guns are pumped down or pulled up the well. This method is primarily used with wireline pump down perforating method of conveyance. This method has the advantage of being a low cost solution, but the disadvantage of being a less accurate means of orienting the charges. As illustrated in FIG. 1b, a gun string is oriented at an angle to the desired orientation. Typical accuracy is at best +/−15 degrees from the desired orientation. Fractures will initiate and propagate in the preferred fracture plane of the formation. Oriented perforating systems can be used to more closely align a plane of perforation tunnels with a preferred fracture plane. Misalignment between the preferred fracture plane and perforations in a well can result in significant pressure drop due to tortuosity in the flow path near the wellbore as shown in FIG. 2a (0230). As generally illustrated in FIG. 2a (0230) and FIG. 2b (0240), a preferred fracture plane (PFP) is shown in relation to perforation orientation of the perforation charges. The perforations that are phased at 90 degrees to the PFP create pinch points resulting in pressure loss and high tortuosity in the flow path. FIG. 2c (0250) illustrates perforations that are at 0 degrees and 180 degrees to the preferred fracture plane and FIG. 2c (0260) shows perforations that are phased at 90 degrees to the PFP.
Hydrocarbon fracturing tunnels have certain preferred orientations where the effectiveness of extracting oil/gas is greatest i.e., when a perforation is aligned along the tunnels, oil/gas flows though the perforation tunnels without taking an alternate path that may become a restrictive path creating high tortuosity conditions.
Therefore, there is a need for a better than +/−15 degrees accuracy to reduce tortuosity and increase well performance.
Prior Art System Internal Orientation Overview (0300)
As generally seen in FIG. 3 (0300), the internal components of the gun are allowed to turn 360 degrees (0720), and are weighted to turn in a preferred direction. The charge case may be part of the weighting mechanism. This method has the advantage of greater accuracy, but can add significant cost to the entire gun assembly, as bearings and rollers are needed to allow rotation of the internal structure with limited available force. In addition, the bearings and rolling mechanism may fail to turn, either through binding from friction or binding due to thermal expansion, or because the gun may be slightly bent due to variation in the well straightness. In this case, the charges may shoot in any random direction and result in well performance worse than may have been achieved with conventional spiral phased charges which require no orientation. Therefore, there is a need to prevent perforation in a random direction used in conventional bearings and roller mechanism.
For a pump down select fire application, full rotation (360°) prevents the use of a through wire to connect subsequent select fire switches to the firing train. The rotating internal components may sever the wire, or require a rotating junction, both of which decrease reliability of the gun system. Therefore there is a need for a limited internal motion gun that would allow the wire to be positioned such that no pinch point exists.
Finally, the bearings and weights required for these systems often reduce the maximum possible charge size, and lower gram weight charges may be needed than would be used in a conventional system of equivalent diameter.
Therefore, there is a need for maximizing charge size in order to achieve maximum perforation efficiency.
In addition, there is a need for maximizing the number of charges by using the length of the perforating guns to maximize shot density.
Furthermore, there is a need for charges to adjust to deviations in the wellbore casing or straightness in perforating gun to orient the charges in a desired orientation for perforation.